Roofing structures can be sloped so that water, such as rainwater, can flow off the roof into a gutter system or directly onto the ground. This reduces the accumulation of water on the roof, which can lead to leaks as water permeates through the roofing structure. Accordingly, the sloped roofing structure serves to remove water from the roof.
Roofing structures often include valleys. In the valley areas of a sloped roofing structure, water is collected from two or more sloped roofing planes or elevations, causing a large volume of water to flow down the valley and into a gutter system, directly onto a lower elevation of the sloped roofing structure, or directly off the roof. In some roofing structures, the valleys can include flashing material extending the length of the valley. The outer edges of the flashing material would also typically be overlapped with the roofing material, such as asphalt shingles, sheet metal, slate, or clay tiles.
Roofing structures also generally have protrusions along a plane. For example, protrusions can include structural walls, chimneys, skylights, mechanical equipment, frames, vents, or any other device or elements that are mounted onto or built into the sloped roofing structure. As water flows down a sloped roofing plane, the protrusions will impede the flow of water causing water to collect against the protrusion and eventually flow around it.
When the flow of water through the valley is heavy, such as from a heavy rainfall, the water can overflow, overshoot, or bypass the gutter system. This causes a condition where water flows directly to the ground and potentially onto people. Alternatively, the falling water can cause damage and/or excessive wear and tear or erosion of property or ground below the valley. For example, the flow of water from the valley can discharge directly onto the ground or a lower elevation roofing material causing unsightly staining or premature aging and deterioration of the surface and possible rotting of the substructure below the surface. Similarly, excessive water flow against the wall of a protrusion will accelerate the degradation of the element that protrudes from the roofing structure.